Light induced nickel plating method for p-type  silicon and n/p solar cell material

ABSTRACT

A simple and fast light induced nickel plating method for p-type silicon wafer and n/p silicon solar cell material is revealed. When a n/p solar cell or p-Si semiconductor substrate, which is subjected to metallization with metal contact on the rear side, is immersed in a plating bath, metal ions are reduced on the front surface of semiconductor as soon as illumination starts on the front. The mechanism of nickel plating in this invention is nickel electroplating under the reduction reaction with the use of interfacial potential between the nickel plating bath and the metal surface. It does not need any surface catalytic processing and extra voltage. Instead, it can carry out the nickel deposition on the specific surface with a high nickel plating rate, a simple process and a low production cost.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a simple and fast light induced nickel plating method for p-type silicon wafer and n/p solar cell material. Particularly, this invention relates to a simple and fast light induced nickel plating method for p-type silicon wafer and n/p silicon solar cell material, which does not need any surface catalytic processing, reducing agent, or applied voltage, but instead can carry out the nickel deposition on the specific surface with high a nickel plating rate, a simple process and a low production cost. The mechanism of nickel plating in this invention is nickel electroplating under the reduction reaction with the use of interfacial potential between the nickel plating bath and the metal surface.

2. Description of Related Art

In the electrode manufacturing process of solar cells, based on the cost consideration, nickel/copper electrode is regarded as a next-generation electrode substituting for screen printing silver electrode. Such a program contains forming first a layer of nickel metallic film, and copper plating using conventional electroplating method after forming a nickel silicide by silicidation. The copper electrode acts as a thickening conductive layer. The copper plating is a mature technology, and therefore a key feature thereof is the nickel coating and the formation of nickel silicide thin layer having palisade local area.

In republished research literatures about nickel/copper electrodes for solar cells, nickel plating methods that have been mentioned include: electroless plating, and light induced plating developed by Fraunhofer ISE and so on. However, these methods have their limitations and shortcomings, so that they are still difficult to be successfully put into mass productions.

The electrodeless nickel plating method is a mature technology. However if applied to the ohmic contact of the semiconductor, it is not proper to be subject to activated palladium processing as a catalytic layer. Surface catalytic processing of electrodeless nickel plating for solar cells is exclusive to some manufacturers as their proprietary technology. The electrodeless plating includes the following disadvantages:

(1) need of being subject to surface catalytic steps;

(2) need of special chemical bath and high cost;

(3) need of an additional heating step (about 80 to 90° C.); and

(4) low plating rate compared to conventional plating.

Fraunhofer ISE in 2009 proposed the light induced plating technology which is regarded as the most promising method. It uses a solar cell to form an n/p junction and screen printed aluminum back electrode. A plating surface (the surface to be plated) is coated with a seed layer. When the light emits on the plating surface and an additional voltage is applied to the aluminum back electrode, a nickel metallic film is deposited on the light-emitted surface (n-type surface). For this reason, the technology still has problems such as need of applying bias and pre-formation of the seed layer.

In order to solve the aforementioned problems, the inventors has studied and proceeded in-depth discussion, and actively seek approaches for many years engaged in the research and experiences of related industries and manufacturing. After long-term research and efforts in development, the inventors has finally the successfully developed this invention “a light induced nickel plating method for p-type silicon wafer and n/p silicon solar cell material” so as to improve the problem encountered in the prior art.

SUMMARY OF THE INVENTION

A main purpose of this invention is to provide a light induced nickel plating method which does not need any surface catalytic processing, reducing agent, or applied voltage, but instead can carry out the nickel deposition on the specific surface with a high nickel plating rate, a simple process and a low production cost.

In order to achieve the above and other objectives, the simple and fast light induced nickel plating method for p-type silicon wafer and n/p silicon solar cell material according to the invention at least includes the following steps:

Step 1: taking a silicon wafer substrate, and forming a layer of aluminum metallic film on a p-type surface thereof after cleaning so as to obtain a plated sample after sintering;

Step 2: formulating a nickel plating bath in a translucent container;

Step 3: cleaning the surface of the plated sample again, and removing a native oxide layer;

Step 4: immersing the plated sample in the nickel plating bath;

Step 5: emitting a light source directly on a plated surface of the plated sample for nickel deposition; and

Step 6: after the scheduled time for the nickel deposition, the light source is removed and the plated sample is taken out to wash and then to dry so that the light-induced nickel plating on the plated sample is completed and a metallic ohmic contact electrode for solar

In one embodiment of the invention, the silicon substrate is of p-type silicon wafer and n/p silicon solar cell material.

In one embodiment of the invention, the container at Step 2 is a translucent container.

In one embodiment of the invention, the nickel plating bath at Step 2 bases on a mixed aqueous solution of nickel chloride and boric acid, and is placed at room temperature while stirring.

In one embodiment of the invention, the light source at Step 5 is a lamp or sunlight.

In one embodiment of the invention, the scheduled time for nickel deposition is one minute to two minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 2 are schematic views of Step 1 according to one embodiment of the invention.

FIG. 3 is a schematic view of Step 2 according to one embodiment of the invention.

FIG. 4 is a schematic view of Step 3 according to one embodiment of the invention.

FIG. 5 is a schematic view of Step 4 according to one embodiment of the invention.

FIG. 6 is a schematic view of Step 5 according to one embodiment of the invention.

FIG. 7 is a schematic view of Step 6 according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The aforementioned illustrations and following detailed descriptions are exemplary for the purpose of further explaining the scope of the present invention. Other objectives and advantages related to the present invention will be illustrated in the subsequent descriptions and appended tables.

FIG. 1 and FIG. 2 are schematic views of Step 1 according to one embodiment of the invention. FIG. 3 is a schematic view of Step 2 according to one embodiment of the invention. FIG. 4 is a schematic view of Step 3 according to one embodiment of the invention. FIG. 5 is a schematic view of Step 4 according to one embodiment of the invention. FIG. 6 is a schematic view of Step 5 according to one embodiment of the invention. FIG. 7 is a schematic view of Step 6 according to one embodiment of the invention. As shown, the present invention provides a simple and fast light induced nickel plating method for p-type silicon wafer and n/p silicon solar cell material at least contains the following steps:

Step 1: taking a silicon substrate 11 of p-type semiconductor or n/p-type semiconductor material, and forming a layer of aluminum metallic film 12 on a p-type surface of the silicon substrate 11 after cleaning so as to obtain a plated sample 1 after sintering (such as the one shown in FIG. 1 and FIG. 2).

Step 2: formulating a nickel plating bath 21 in a translucent container 2 (as shown in FIG. 3), wherein the nickel plating bath 21 bases on a mixed aqueous solution of nickel chloride and boric acid, and is placed at room temperature while stirring.

Step 3: cleaning the surface of the plated sample 1 again (as shown in FIG. 4), and removing a native oxide layer.

Step 4: immersing the plated sample 1 in the nickel plating bath 21 inside the container 2 (as shown in FIG. 5).

Step 5: emitting a light source 3 directly on a plated surface 13 of the plated sample 1 (as shown in FIG. 6) for nickel deposition. The light source 3 can be a lamp or sunlight.

Step 6: After one minute to two minutes of the scheduled time for the nickel deposition, the light source 3 is removed and the plated sample 1 is taken out to wash and then dry. Thereby, the light-induced nickel plating on the plated sample is completed and a metallic ohmic contact electrode 4 for solar cell is obtained (as shown in FIG. 7).

Taking advantages of traditional electroplating and electroless plating, the present invention can be applied to solar cells and other optoelectronic components, and produces the metallic film as the ohmic contact or the semiconductor buffer layer.

The present invention at least offers the following advantages:

1. The light induced nickel plating (LINP) technology pre-forms the aluminum metallic film 12 on the p-type surface of the silicon substrate 11 (p-type silicon wafer or n/p junction silicon solar cell) which is immersed in the nickel plating bath 21. When the light source directly emitted onto the surface to be plated with nickel, the nickel-plating reaction triggers. The invention has the simple and rapid process without the need of adding extra voltage.

2. When the aluminum metallic film 12 and the nickel plating bath 21 are at equilibrium, there forms an interface potential difference between the surface of the aluminum metallic film 12 and the nickel plating bath 21. Meanwhile, there also forms a potential difference between the surface of the silicon substrate 11 and the nickel plating bath 21. The sum of these two potential differences can achieve the required potential difference for nickel deposition. The principle of nickel plating in this invention is nickel electroplating, rather than the reduction of the chemical solution itself. So the rate of the nickel plating is fast (about 1 minute to 2 minutes), a nickel metallic film of about 1 μm in thickness will be obtained.

3 The plating surface, i.e. the surface to be plated, in this invention does not need to go through any of the catalytic processing, simplifying the process of nickel plating.

4. The nickel deposition occurs only on the semiconductor surface, not on the aluminum metallic film 12. Therefore there is no need of more one procedure to protect the back surface, further simplifying the nickel plating process

5 The nickel plating bath 21 in this invention uses a mixed aqueous solution of nickel chloride and boric acid. The composition of the bath is simple.

6. The present invention can obtain a high-quality nickel metallic film.

In summary, the present invention is simple and fast to carry out the nickel plating process for p-type silicon wafer and n/p silicon solar cell material by light induced plating. It can effectively improve the shortcomings of conventional technology without any surface catalytic processing and extra voltage. The process is simple and the production cost is low, making the invention more progressive and more practical in use which complies with the patent law.

The descriptions illustrated supra set forth simply the preferred embodiments of the present invention; however, the characteristics of the present invention are by no means restricted thereto. All changes, alternations, or modifications conveniently considered by those skilled in the art are deemed to be encompassed within the scope of the present invention delineated by the following claims. 

What is claimed is:
 1. A simple and fast light induced nickel plating method for p-type silicon wafer and n/p silicon solar cell material at least comprising the following steps: Step 1: taking a silicon substrate, and forming a layer of aluminum metallic film on a p-type surface thereof after cleaning so as to obtain a plated sample after sintering; Step 2: formulating a nickel plating bath in a translucent container; Step 3: cleaning the surface of the plated sample again, and removing a native oxide layer; Step 4: immersing the plated sample in the nickel plating bath; Step 5: emitting a light source directly on a plated surface of the plated sample for nickel deposition; and Step 6: after the scheduled time for the nickel deposition, the light source is removed and the plated sample is taken out to wash and then to dry so that the light induced nickel plating on the plated sample is completed and a metallic film on silicon substrate is obtained.
 2. The method of claim 1, wherein the silicon substrate is of p-type silicon wafer and n/p silicon solar cell material.
 3. The method of claim 1, wherein the container at Step 2 is a translucent container.
 4. The method of claim 1, wherein the nickel plating bath at Step 2 bases on a mixed aqueous solution of nickel chloride and boric acid, and is placed at room temperature while stirring.
 5. The method of claim 1, wherein the light source at Step 5 is a lamp or sunlight.
 6. The method of claim 1, wherein the scheduled time for nickel deposition is one minute to two minutes. 